1. Field of the Invention
The present invention relates to a method and system for data migration between different database systems and to a computer-readable medium encoded with a program designed for such data migration. More particularly, the present invention relates to a method and system for data migration from a database constructed with a network data model to another database constructed with a relational data model, as well as to a computer-readable medium encoded with a program that causes a computer to execute such a data migration process.
2. Description of the Related Art
The database technology plays a key role in today's integrated information systems. Modern database designs can be distinctively categorized in terms of the data model used to organize individual records, e.g., network model and relational model. Historically, network data models have long been used as the basis for many commercial systems. However, many of today's system developments are based on the relational data model because of its advantages over the past models, including comprehensible data structure, high data independence, and non-procedural data manipulations. While there still exist a number of applications working on the basis of the network data model, it is not easy to maintain those systems because they need a thorough knowledge of how the data is actually linked to each other in the network structure. In reality, the number of engineers who can support those systems are decreasing, and this fact causes users' concerns about the operations and maintenance of their database systems. In such situations, many legacy systems based on the network data model are now required to migrate to new relational database systems.
In the network data model, the relations between records are represented by pointers under the control of a database management system (DBMS). As opposed to this, data in the relational data model is organized in the form of simple data tables, where the data items, or records, in each table have no hierarchical relationships with one another.
The information about pointers in the network data model is affixed to each record as "set information" that shows its hierarchical relationships with other records. However, this set information cannot be added as is to the records of the relational model because it is not directly specified by the users in an explicit manner, and the relational data model does not allow, by definition, any hierarchical relationships between records. Although it would be possible to transfer individual records to a new database environment, their record-to-record connections cannot directly be transported from network data model to relational data model. Therefore, when trying to migrate database systems from network model to relational model, it is necessary to analyze the structure of the existing data and make an appropriate modification to make the data suitable for the new database design.
However, the changes in the data structure will affect the total processing mechanisms implemented in application programs (hereafter "applications") to manipulate the data. While it is easily understood that the existing applications would not operate unless they are properly modified, what the migration from network model to relational model entails is not a partial modification, but extensive work for adaptation to the new data structure. Eventually, one has to discard the existing applications and develop other applications to provide the same functions on the new database designs. As such, the data migration is not a simple data conversion, but rather a redesign of total database systems from scratch, requiring a long development time, a large amount of work, and considerable labor costs.